Geographic Range

Mountain beavers are found in North America. The two main ranges of mountain beavers are from Merritt, British Columbia to Rio Dell, California and from Mt. Shasta, California to western Nevada. There are also sparse populations of this species on the Californian coast (Carraway, 1993).

Habitat

The habitat of mountain beavers ranges from forested areas at sea level to timberline peaks. They enjoy areas that contain second growth tree species, shrubs, and prefer to be near water. They are most abundant in high mountain peaks with decidous forest and are least common in coniferous forests. Mountain beavers must live in places with deep soils in order to construct their burrow system. (Carraway, 1993).

Physical Description

Mountain beavers are dark brown except for a white spot below each ear. They have strong incisors. Their head is flat and wide and their nose is slightly arched. The body is thick, heavy, and covered with coarse, dull fur. Underneath the fur is a sparse covering of guard hair, which is dark red of grayish brown in color. They have short limbs and their total length is 300 - 470 mm (Carraway, 1993).

Reproduction

Beginning in November or December, there is an increase in the size of the testes, prostate and bulbourethal glands of males. As females reach estrous, their nipples increase in size, their vulva swell, and vaginal smears reveal predominately ephithelial cells. Females that are only a year old ovulate as well but no breeding occurs, demonstrating that ovulation is spontaneous instead of being triggered by copulation. The onset of the estrous cycle is around February or March.

Gestation usually lasts six to eight weeks and litters of two to three young are common. The weight of the young beavers is 25.5g. At birth, the beavers are pink, helpless, blind, and do not have a considerable covering fur. Within six to eight weeks the beavers are able to function (Carraway, 1993).

Behavior

Mountain beavers are not very social animals. Rarely do they go farther than a few meters from their burrows. Their home ranges overlap and each beaver defends its nest site. The sight and the hearing of the mountain beaver are very poor but their senses of smell and touch are well developed. Mountain beavers vocalize in the form of whistles and booming sounds. They also squeal while fighting and make a grinding noise with their teeth (Carraway, 1993).

The burrow system of mountain beavers is centered around the nest sites. Almost all the entrances are connected to the underground nest chambers. The nest chambers are carpeted with dried leaves. The opening to the tunnels are covered with tent like stick structure or have vegetation covering the opening (Carraway, 1993).

Communication and Perception

Food Habits

Mountain beavers are herbivorous animals; their diet includes forbs, grasses, and even ferns such as sword fern and bracken fern. The composition of the diet of mountain beavers differs depending on the sex and age of the individual and the season. While they are eating, they squat and emit hard and soft fecal pellets which they catch in their mouths. The hard pellets are put into a pit next to the vegetation while the soft pellets are reingested (Carraway, 1993).

Economic Importance for Humans: Negative

Foraging by the mountain beavers on seedlings in areas undergoing reforestation can lead to environmental and economic damage. They also cause garden damage and raid the crops of farmers. To prevent further damage by the mountain beavers, people take various types of action. One is to reduce the food consumed by mountain beavers by using herbicides and burning. Another method is to control the population directly by traps or through using toxic baits. Plastic mesh has also been put around trees that the mountain beavers destroy. These prevention measures add to a considerable amount of money (Carraway, 1993).

Conservation Status

The IUCN lists the subspecies A.r. nigra and A.r. phaea of the mountain beaver as indeterminate (Wilson, 1993).

Contributors

Toni Lynn Newell (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.